Hypotheses: Southern Right Whale Mortality

Nutritional Deficiencies

One hypothesis for the rise in southern right whale calve mortalities off the coast of Argentina is that a lack of proper nutrition is causing pregnant whales to produce less healthy offspring. Southern right whales normally feed on the Patagonian Shelf, and then travel to waters south of 50°S to feed on swarms of Antarctic Krill. However, since the year 2000, more southern right whales appear to be feeding primarily on copepods on the Patagonian Shelf. This shift in diet may be causing nutrient deficiencies.

Infectious Diseases

Infectious diseases could potentially be causing whales to die. Post-mortem examinations called necropsies are conducted to test for pathogens and physical responses to disease. Dr. Uhart says, “We haven’t found any indication that infectious diseases are a huge issue here.” Studies will continue to monitor the health of the whale population. “New technologies might allow us to find pathogens we might have overlooked or been unable to identify in the past,” Dr. Uhart adds.

Toxins

A third hypothesis is that whale death could be the result of biotoxins released by algal blooms. This hypothesis emerged in response to the deaths in 2005 and 2007, which looked like poisoning events because they occurred within a short period of time, late in the season, and coincided with major algal blooms at the Península. Dr. Uhart says, “The algal blooms are occurring; we just don’t have a clear indication that the whales are ingesting toxins and that they are contributing to their death.” Only traces of toxins were found in a few whales, “but that is definitely another thing that we are exploring and continue to monitor,” she says.

Scientists have also researched toxins like heavy metals and pesticides to see if they might be the cause of the problem. The results of these studies indicate that chemical toxin levels in the whales’ tissues are relatively low, and thus are not responsible for the rise in whale mortality.

Kelp Gull Attacks

Kelp gulls have learned to feed on the skin and blubber that they peck from the backs of living southern right whales at Península Valdés. Read more and watch video here. - By Jasjeet Dhanota